Bicycle rear suspension

ABSTRACT

A bicycle rear suspension linkage system comprising an elongate seat tube having an upper pivot mount rigidly attached to the upper end thereof and an axle receiving bracket rigidly attached to the lower end thereof. An upper rocker is pivotally connected to the upper pivot mount with a lower rocker being pivotally connected to a lower pivot mount rigidly attached to the axle receiving bracket. The linkage system further comprises pairs of seat stay and chain stay members, with the upper ends of the seat stay members being pivotally connected to the upper rocker and the front ends of the chain stay members being pivotally connected to the lower rocker. Additionally, the back ends of the chain stay members are pivotally connected to the lower ends of the seat stay members. Also provided is a shock absorber having a body portion and a reciprocal piston rod, the distal end of which is pivotally connected to the upper pivot mount. Pivotally connected to and extending between the upper rocker and body portion of the shock absorber is a pair of upper link rods, while rigidly attached to the body portion is an elongate alignment rod. Pivotally connected to and extending between the lower end of the alignment rod and the front ends of the chain stay members is a lower link rod.

FIELD OF THE INVENTION

The present invention relates generally to bicycles, and moreparticularly to a rear suspension system for a bicycle frame whichpossesses shock absorption characteristics and is adapted to notadversely affect the performance of the bicycle.

BACKGROUND OF THE INVENTION

The primary structural component of a bicycle is the bicycle frame.Typically, the bicycle frame comprises an elongate cross bar which isrigidly secured to and extends between a head tube of the bicycle and aseat tube of the bicycle. The heat tube typically provides a structuralbase for the stem of the bicycle to which the handlebars are attached.The seat tube provides a base for a seat post which is generallytelescopically received therewithin and to which is secured the saddleor seat of the bicycle. In typical bicycle frame construction, the seattube includes a generally cylindrically axle-receiving bracket attachedto the lower end thereof which is adapted to receive the bottom bracketaxle. The bottom bracket axle typically extends between andinterconnects the cranks to which are attached the pedals. Rigidlysecured to and extending between the head tube and the cylindricalaxle-receiving bracket is an elongate down tube.

In addition to the aforementioned structural components, rigidly securedto and extending rearwardly from the axle-receiving bracket are firstand second chain stay members. Additionally, rigidly secured to andextending downwardly from the upper end of the seat tube are first andsecond seat stay members having distal ends which are rigidly secured tothe back ends of the first and second chain stay members. Typically, thedistal ends of the seat stay members and back ends of the chain staymembers are interconnected in a manner adapted to receive the rear tireaxle of the bicycle.

The foregoing description generally represents the construction ofconventional prior art bicycle frames. Typically, once such prior artframes are constructed, the aforementioned structural components arerigidly secured to one another through the use of welding or brazingtechniques. Though this method of constructing the bicycle frameprovides the resulting frame with structural integrity, the bicycleframe does not possess a suspension having shock absorbingcharacteristics. As will be recognized, the ride, comfort andperformance of the bicycle would be greatly enhanced if the bicycleframe were adapted to at least partially accommodate the shocksroutinely encountered while riding the bicycle.

Though recent prior art bicycle frames include front and/or rear shockabsorbing assemblies, such bicycle frames possess certain deficiencieswhich detract from their overall utility. In this respect, the manner inwhich the rear shock absorbing assemblies are typically interfaced tothe seat stay members of the frame creates a significant amount oflateral instability for the rear wheel of the bicycle. As will berecognized, such instability severely diminishes the performance andhandling characteristics of the bicycle. Additionally, many currentlyknown rear shock absorbing assemblies create slop within the chainduring normal and vigorous pedaling, thus adversely affecting theperformance of and speed obtainable with the bicycle. Further, in mostprior art rear shock absorbing assemblies, the rear axle pivots about asingle point when subjected to a shock force which results in thepedaling forces either compressing or extending the shock absorber ofthe rear suspension, and/or the rear tire axle moving in a directionother than parallel to the direction of the shock force applied to therear wheel. In this respect, when the shock absorber of the rearsuspension is affected by the pedal force, some of the riders' energy isneedlessly wasted to activate the shock absorber. Additionally, when therear tire axle moves in an arc that is not tangent to the direction ofthe shock force applied to the rear wheel, riding efficiency is lost.

As previously specified, the rear suspension is often affected by thepedal force, thus causing some of the rider's energy to be needlesslywasted. In this respect, a problem common to most prior art rearsuspension systems is the tendency of the rear suspension system toeither lock-up or "squat" when the rider pedals aggressively. Sincethese prior art rear suspension systems are generally designed having asingle lever arm which pivots about a single point, the lock-up or squatgenerally occurs as a result of chain tension acting on the single leverarm. If the single pivot point of the rear suspension system is abovethe chain line, the system will typically lock-up, thereby providingsuspension only when the shock or bump force exceeds the chain tension.Conversely, if the single pivot point of the rear suspension system isbelow the chain line, the system will typically squat since the chaintension is acting to compress the shock absorber of the rear suspensionsystem in the same manner as does the shock or bump force. The presentinvention specifically overcomes these and other deficiencies associatedwith prior art bicycle frames.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention,there is provided a shock absorbing bicycle rear suspension linkagesystem which is adapted to provide the bicycle frame and hence thebicycle with enhanced riding comfort and performance. The bicycle rearsuspension linkage system generally comprises an elongate seat tubehaving an upper pivot mount rigidly attached to the upper end thereof,and an axle receiving bracket rigidly attached to the lower end thereof.Rigidly attached to the axle receiving bracket is a lower pivot mount.Additionally, pivotally connected to the upper pivot mount is an upperrocker, while pivotally connected to the lower pivot mount is a lowerrocker.

The linkage system further comprises first and second seat stay membershaving upper ends which are rigidly attached to a seat stay end housingand first and second chain stay members having front ends which arerigidly attached to a chain stay end housing. The seat stay end housingis pivotally connected to the upper rocker, with the chain stay endhousing being pivotally connected to the lower rocker. Additionally, theback ends of the chain stay members are pivotally connected to the lowerends of the seat stay members. Rigidly attached to the lower ends of theseat stay members are a pair of rear tire axle receiving members.

Also included in the rear suspension linkage system is a shock absorbercomprising a body portion and a reciprocable piston rod which extendsaxially from an upper end of the body portion which has a distal endpivotally connected to the upper pivot mount. In addition to the bodyportion and piston rod, the shock absorber further comprises a springmember which extends between the upper pivot mount and the body portion,with the piston rod extending axially through the spring member.Extending between the upper rocker and shock absorber are first andsecond upper link rods which have top ends pivotally connected toopposed sides of the upper rocker and bottom ends pivotally connected toopposed sides of the body portion of the shock absorber.

The rear suspension linkage system further comprises an elongatealignment rod having a proximal end threadably attached to the lower endof the shock absorber body portion in a manner wherein the alignment andpiston rods are coaxially aligned. Also provided is a lower link rodwhich has a first end pivotally connected to the distal end of thealignment rod, and a second end which is pivotally connected to thechain stay end housing. In the preferred embodiment, the alignment rodextends through and is guided by at least one, and preferably a pair ofalignment bushings which are rigidly attached to the seat tube.Additionally, the coaxially aligned alignment and piston rods preferablyextend in parallel relation to the seat tube.

To maintain the linkage system in tension, the seat stay members andupper rocker are adapted to have a greater mechanical advantage inpulling upwardly on the first and second upper link rods alignment rodand lower link rod than the lower rocker has in pulling downwardly onsuch components. When the rear wheel is subjected to a shock force, theupper rocker is caused to pivot upwardly, which in turn causes the firstand second upper link rods to be pulled upwardly. The upward movement ofthe upper link rods causes the alignment rod and hence the lower linkrod to be pulled upwardly, which in turn facilitates the upward pivotalmovement of the lower rocker. Advantageously, the upward pivotalmovement of the lower rocker concurrently with the upward pivotalmovement of the upper rocker allows the rear axle to move upwardly in avertical direction when the shock force is applied to the rear wheel.Due to the connection of the upper link rods and alignment rod to theshock absorber, the amount of movement of the linkage system iscontrolled and limited thereby, with the spring member of the shockabsorber being operable to dampen the shock force applied to the rearwheel.

BRIEF DESCRIPTION OF THE DRAWINGS

These, as well as other features of the present invention, will becomemore apparent upon reference to the drawings wherein:

FIG. 1 is a perspective view of a bicycle incorporating the rearsuspension linkage system constructed in accordance with the presentinvention;

FIG. 2 is a side elevational view of the bicycle frame incorporating therear suspension linkage system of the present invention;

FIG. 3 is an enlarged perspective view of a portion of the rearsuspension linkage system of the present invention; and

FIG. 4 is an exploded view of the rear suspension linkage system shownin FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for purposes ofillustrating a preferred embodiment of the present invention only, andnot for purposes of limiting the same, FIG. 1 perspectively illustratesa bicycle 10 incorporating a bicycle frame 12 constructed to incorporatethe bicycle rear suspension and linkage system of the present invention.The bicycle frame 12 generally comprises a head tube 14 disposed at thefront end of the bicycle 10 and a seat tube 16 disposed toward the rearend of the bicycle 10. Connected to the top end of the head tube 14 is astem 18 to which is attached the handlebars 20. Connected to the bottomend of the stem 18 is a conventional front shock absorber assembly 22defining a first fork 24 and a second fork 26 between which is mountedthe axle 28 of the front wheel 30. Importantly, the front shock absorberassembly 22 is adapted to provide the impressive first fork member 24and compressive second fork member 26 with shock absorbing capability.Telescopically received into the top end of the seat tube 16 is a seatpost 32 having a saddle or seat 34 connected thereto.

Rigidly attached to and extending between the head tube 14 and seat tube16 is an elongate cross bar 36. Additionally, rigidly attached to thebottom end of the seat tube 16 is an axle receiving bracket 38 having anaxle receiving bore 40 extending axially therethrough. In the preferredembodiment, the axle receiving bracket 38 has a generally cylindricalconfiguration and is attached to the lower end of the seat tube 16 via abrazed or welded connection. The bore 40 of the axle receiving bracket38 is sized and configured to receive a bottom bracket axle of thebicycle 10. Attached to the opposed ends of the bottom bracket axle arefirst and second cranks 42 to which are attached pedals 44.Additionally, attached to one end of the bottom bracket axle between thebottom bracket axle and a crank 42 is a main sprocket 46 which isadapted to rotate concurrently with the bottom bracket axle. Rigidlyattached to and extending between the head tube 14 and the axlereceiving bracket 38 is an elongate down tube 48. In the preferredembodiment, head tube 14, cross bar 36, axle receiving bracket 38, anddown tube 48, each have generally cylindrical configurations and aresecured to one another via welded or braised connections.

Referring now to FIGS. 2-4, rigidly attached to the rear portion of theupper end of the seat tube 16 is an upper pivot mount 50. Additionally,rigidly attached to the lower portion of the axle receiving bracket 38is a lower pivot mount 52. In the preferred embodiment, the upper pivotmount 50 includes a pair of ear portions 54 defining a spacetherebetween. Extending laterally through the ear portions 54 areapertures 56 which are disposed in coaxial alignment. Additionally,extending through the lower pivot mount 52 is an aperture 58. In thepreferred embodiment, the upper pivot mount 50 and lower pivot mount 52are attached to the seat tube 16 and axle receiving bracket 38,respectively, via a welding or brazing process.

Pivotally connected to the upper pivot mount 50 is an upper rocker 60,while pivotally connected to the lower pivot mount 52 is a lower rocker62. In the preferred embodiment, the upper rocker 60 defines a frontpair of mounting ears 64, a back pair of mounting ears 66, and anintermediate pair of mounting ears 68. Extending laterally through thefront pair of mounting ears 64 are apertures 70 which are disposed incoaxial alignment, while extending laterally through the back pair ofmounting ears 66 are apertures 72 which are also disposed in coaxialalignment. Additionally, extending laterally through the intermediatepair of mounting ears 68 are apertures 74 which are also disposed incoaxial alignment, although separated by the central portion of theupper rocker 60. Similar to the upper rocker 60, the lower rocker 62defines a front pair of mounting ears 76 having a coaxially aligned pairof apertures 78 extending laterally therethrough, and a back pair ofmounting ears 80 having a coaxially aligned pair of apertures 82extending laterally therethrough. In the preferred embodiment, the upperrocker 60 is pivotally connected to the upper pivot mount 50 via thereceipt of the ear portions 54 of the upper pivot mount 50 into thespace defined between the front pair of mounting ears 64 of the upperrocker 60. In this respect, the distance separating the front pair ofmounting ears 64 is adapted to slidably accommodate the ear portions 54of the upper pivot mount 50. Importantly, the ear portions 54 areoriented between the front pair of mounting ears 64 such that the pairof apertures 56 disposed between the ear portions 54 are coaxiallyaligned with the pair of apertures 70 disposed within the mounting ears64. Thereafter, a fastener 84 is inserted through the coaxially alignedapertures 56, 70 thus pivotally connecting the upper rocker 60 to theupper pivot mount 50. To facilitate the pivotal connection of the lowerrocker 62 to the lower pivot mount 52, the lower pivot mount 52 isreceived into the space defined between the front pair of mounting ears76 of the lower rocker 62. Like the pair of mounting ears 64 previouslydescribed, the distance separating the mounting ears 76 from each otheris such that the lower pivot mount 52 may be slidably receivedtherebetween. The lower pivot mount 52 is oriented between the mountingears 76 such that the pair of apertures 78 are coaxially aligned withthe aperture 58 of the lower mount 52. Thereafter, as seen in FIG. 3, afastener 86 is extended through the coaxially aligned apertures 78, 58,thus pivotally connecting the lower rocker 62 to the lower pivot mount52.

The bicycle frame 12 of the present invention further comprises firstand second seat stay members 88, 90 which have upper ends rigidlyattached to a seat stay end housing 92. The seat stay end housing 92defines a bore 94 extending longitudinally therethrough, and ispivotally connected to the upper rocker 60. In this respect, the seatstay end housing 92 is received into the space defined between the backpair of mounting ears 66 of the upper rocker 60 which are spaced fromeach other a distance sufficient to allow the seat stay end housing 92to be slidably received therebetween. The end housing 92 is orientedbetween the mounting ears 66 such that the apertures 72 of the mountingears 64 are coaxially aligned with the bore 94. Thereafter, a fastener96 is extended through the coaxially aligned apertures 72 and board 94,thus pivotally securing the end housing 92 to the upper rocker 60.

The bicycle frame 12 further includes first and second chain staymembers 96, 98 which have front ends rigidly attached to a chain stayend housing 100. Like the end housing 92, the chain stay end housing 100defines a bore 102 extending longitudinally therethrough and ispivotally connected to the lower pivot mount 52. In this respect, theback pair of mounting ears 80 of the lower rocker 62 are separated fromeach other a distance sufficient to allow the end housing 100 to beslidably received into the space defined between the mounting ears 80 ina manner wherein the apertures 82 of the mounting ears 80 are coaxiallyaligned with the bore 102 of the end housing 100. Thereafter, a fastener104 is inserted into the coaxially aligned apertures and bore 102, thuspivotally connecting the end housing 100 to the lower rocker 62. In thepreferred embodiment, the upper ends of the seat stay members 88, 90 andthe front ends of the chain stay members 96, 98 are attached to theirrespective end housings 92, 100 via a welding or brazing process.

In the preferred embodiment, the back ends of the chain stay members 96,98 are pivotally connected to the lower ends of the seat stay members88, 90. Particularly, the back end of the first chain stay member 96 ispivotally connected to the lower end of the first seat stay member 88,with the back end of the second chain stay member 98 being pivotallyconnected to the lower end of the second seat stay member 90. Rigidlyattached to the lower ends of the first and second seat stay members 88,90 is a pair of rear tire axle receiving members 106 which are adaptedto support the rear tire axle 108 of the rear wheel 110 therebetween.Attached to one end of the rear tire axle 108 is a rear sprocket 109which is cooperatively engaged to the main sprocket 46 via a chain 111.

One of the primary components of the bicycle frame 12 is a shockabsorber 112. In the preferred embodiment, the shock absorber comprisesa tubular body portion 114 having a reciprocable piston rod 116extending axially from its top end, and a mounting bracket 118 attachedto and extending downwardly from its bottom end. As best seen in FIGS. 3and 4, a portion of the outer surface of the body portion 114 adjacentthe upper end thereof is threaded so as to allow a lower springretention member 120 to be threadably received onto the body portion114. Additionally, rigidly attached to the distal end of the piston rod116 is an upper spring retention member 122 including an internallythreaded stem 124 formed on the upper surface thereof. Threadablyreceived into the stem 124 is a coupling member 126 including anaperture 128 extending laterally through a circular portion thereof. Theshock absorber 112 further comprises a helical spring member 130disposed between the upper and lower spring retention members 120, 122,in a manner wherein the upper end of the spring member 130 abuts thelower surface of the upper spring retention member 122, the lower end ofthe spring member 130 abuts the top surface of the lower springretention member 120, and the piston rod 116 of the shock absorber 112extends axially through the center of the spring member 130. As will berecognized, the tension of the spring member 130 is selectivelyadjustable via the selective placement of the lower spring retentionmember 120 on the threaded outer surface portion of the body portion114.

As best seen in FIG. 3, the coupling member 126, and hence the pistonrod 116, is pivotally connected to the upper pivot mount 50. In thisrespect, the coupling member 126 is sized so as to be slidablyreceivable into the space defined between the ear portions 54 of theupper pivot mount 50 in a manner wherein the apertures 56 of the earportions 54 are coaxially aligned with the aperture 128 of the couplingmember 126. As previously specified, the upper rocker 60 is alsopivotally connected to the upper pivot mount 50 via the receipt of thefastener 84 into the coaxially aligned apertures 70 and 56. As such, inthe preferred embodiment, the fastener 84 is utilized to pivotallyinterconnect the upper pivot mount 50 to the upper pivot mount 60 andcoupling member 126 via the extension thereof through the coaxiallyaligned apertures 70, 56 and 128. As best seen in FIG. 4, the mountingbracket 118 includes a hub 132 formed along the back vertical edgethereof and including an aperture 134 extending laterally therethrough.

The bicycle frame 12 further comprises first and second upper link rods136, 138 which are used to pivotally connect the upper rocker 60 to themounting bracket 118 of the shock absorber 112. The first and secondupper link rods 136, 138 are identically configured and includeapertures 140 disposed in their upper ends, and apertures 132 disposedin their lower ends. In the preferred embodiment, the upper link rods136, 138 are sized such that the upper ends thereof are slidablyreceivable into respective spaces defined between the intermediate pairof mounting ears 68 and the main body portion of the upper rocker 60 ina manner wherein the apertures 140 disposed within the upper ends arecoaxially aligned with the apertures 74 disposed within the mountingears 68. Thereafter, a fastener 144 is extended through the coaxiallyaligned apertures 74, 140 as well as an aperture (not shown) extendingthrough the main body portion of the upper rocker 60 in coaxialalignment with the apertures 74, 140, thus pivotally connecting theupper link rods 136, 138 to the upper rocker 60. The bottom ends of theupper link rods 136, 138 are then oriented over the opposed planar sidesof the mounting bracket 118 such that the apertures 142 are coaxiallyaligned with the aperture 134 extending through the hub 132. Thereafter,a fastener 146 is extended through the coaxially aligned apertures 142,134 thus pivotally securing the lower ends of the upper link rods 136,138 to the mounting bracket 118, and hence the shock absorber 112.Importantly, the fastener 146 is also extended between a pair of sleeves148 which are sized and adapted to cover the exposed portions of thefastener 146 extending between the bottom ends of the upper link rods136, 138 and mounting bracket 118. The sleeves 148 each have a tubularconfiguration.

Rigidly attached to and extending downwardly from the shock absorber 12,and more particularly the mounting bracket 118, is an elongate alignmentrod 150. In the preferred embodiment, the upper end of the alignment rod150 is externally threaded so as to be threadably receivable into aninternally threaded aperture (not shown) disposed within the bottomsurface of the mounting bracket 118. Importantly, the alignment rodaperture disposed in the bottom surface of the mounting bracket 118 isoriented such that the alignment rod 150 is coaxially aligned with thepiston rod 116 of the shock absorber 112 when threadably receivedthereinto. Formed on the lower end of the alignment rod 150 is anenlarged head portion 152 which includes an aperture 154 extendinglaterally therethrough. In the preferred embodiment, the alignment rod150 is extended through and is guided by at least one, and preferably apair of alignment bushings 156. Each of the alignment bushings 156 aredisposed within alignment brackets 158 which are rigidly attached to arear portion of the seat tube 116 via a welding or brazing process. Aswill be recognized, the threaded upper end of the alignment rod 150 isextended upwardly through the lower and upper alignment bushings 156 insuccession, prior to being threadably received into the alignment rodmounting aperture. Each of the alignment bushings 156 includes anenlarged head portion overlying the top surface of a respectivealignment bracket 158. In the preferred embodiment, when the alignmentrod 150 is extended through the alignment bushings 156 and threadablyattached to the mounting bracket 118, the alignment rod 150 and pistonrod 116 which are coaxially aligned will also extend in generallyparallel relation to the seat tube 116.

The final component comprising the rear suspension linkage system is alower link rod 160 having a top end including an aperture 162 extendingtherethrough, and a bottom end having an aperture 164 extendingtherethrough. In the preferred embodiment, the top end is pivotallyconnected to the head portion 152 of the alignment rod 150 by coaxiallyaligning the apertures 162, 154 and extending a fastener 166therethrough. The lower end of the lower link rod 160 is pivotallyconnected to an extension 168 which is rigidly attached to and extendsupwardly from a central portion of the chain stay and housing 100 andincludes an aperture 170 extending therethrough. In this respect, thepivotal connection between the lower link rod 160 and extension 168 isfacilitated by coaxially aligning the apertures 164, 170, and extendinga fastener 172 therethrough.

As previously specified, in most prior art rear suspension systems, therear axle of the rear wheel pivots about a single point which typicallycauses the pedaling forces to compress or extend the suspension and/orthe rear wheel axle to move in a motion other than parallel to thedirection of the force being applied to the rear wheel. In those caseswherein the suspension is affected by the pedal force, a portion of therider's energy is wasted since such energy is used to needlesslyactivate the shock absorber of the rear suspension. Additionally, if therear tire axle moves in an arc that is not tangent to the direction ofthe shock force applied to the rear wheel, efficiency is lost.Importantly, the various components comprising the rear suspension andlinkage system of the present invention as previously described areadapted to provide a suspension for the rear wheel 110 of the bicycle 10that is negligibly affected by the pedaling force, and allows the rearaxle 108 to move in a direction which is substantially parallel to thedirection of the shock force exerted to the rear wheel 110 when suchencounters a bump or other obstruction.

Referring now to FIGS. 1-3, when a shock force is applied to the rearwheel 110 of the bicycle 10, due to the attachment of the rear tire axlereceiving members 106 to the seat stay members 88, 90, the seat staymembers 88, 90 are caused to pivot upwardly in the direction A. Theupward pivotal movement of the seat stay members 88, 90 in turn causesthe upper rocker 60 to pivot upwardly in the direction B shown in FIG.2. As will be recognized, the upward pivotal motion of the upper rocker60 serves to pull the first and second upper link rods 136, 138 upwardlyin the direction C, thus facilitating the compression of the helicalspring member 130 between the upper and lower spring retention members120, 122. The upward pulling of the upper link rods 136, 138 also causesthe alignment rod 150 to be pulled upwardly in the direction D throughthe alignment bushings 156, which in turn causes the lower link rod 160to be pulled upwardly in the direction E. The upward pulling of thelower link rod 60 in the direction E causes the lower rocker 62 to pivotupwardly in the direction F. Advantageously, due to the structure of therear suspension and linkage system, the concurrent upward pivoting ofthe upper rocker 60 in the direction B and the lower rocker 62 in thedirection F causes the rear axle receiving brackets 106 and hence therear axle 108 and rear tire 110 to move generally vertically upwardly inthe direction G when subjected to a shock force, rather than moving inan arc which facilitates lost efficiency.

In the preferred embodiment, the upper rocker 60 and seat stay members88, 90 pivotally connected thereto are adapted to have a greatermechanical advantage on the connecting linkage comprising the shockabsorber 112, upper link rods 136, 138, alignment rod 150 and lower linkrod 160, then does the lower rocker 62 and pivotally connected chainstay members 96, 98. In this respect, the adapting of the upper rocker60 and seat stay members 88, 90 to possess the greater mechanicaladvantage serves to control the action of the remaining components ofthe linkage system and assures that the linkage assembly is nearlyalways in tension. As previously specified, the upward movement in thedirection C of the upper link rods 136, 138 as caused by the upwardpivotal movement in the direction B of the upper rocker 60 is controlledand limited by the shock absorber 112. In this respect, the shockabsorber 112 is adapted to dampen some of the shock force exerted on therear tire 10 as such force is transmitted through the linkage assembly.In this respect, the degree of the shock force absorbed by the shockabsorber 112 may be selectively adjusted via the positioning of thelower spring retention member 120 along the threaded outer surfaceportion of the body portion 114.

As also previously specified, most prior art rear suspension systems aredesigned having a single lever arm which pivots about a single point. Inthis respect, these rear suspension systems have the tendency to eitherlock up or squat when the rider pedals aggressively, which occurs as aresult of the chain tension acting on the single lever arm of thesystem. If the single pivot point is above the chain line, the rearsuspension system will typically lock-up, thereby providing suspensiononly when the shock force exceeds chain tension. Conversely, if thesingle pivot point is below the chain line, the rear suspension systemwill typically squat since the chain tension is acting to compress theshock absorber in the same manner as a shock force.

In the present linkage assembly, the application of a shock force to therear wheel 110 tends to move the rear wheel 110 in the upward verticaldirection G, and pivot the upper and lower rockers 60, 62 upwardly inthe directions B, F. However, in the preferred embodiment, the upper andlower rockers 60, 62 and alignment rod 150 are specifically orientedsuch that chain tension, occurring as a result of pedaling, tends toforce the upper and lower rockers 60, 62 in opposite directions therebyproducing pure tension in the alignment rod 150 and causing no influencein the vertical travel of the rear wheel 110 in the direction G. In thisrespect, when the bicycle 10 is vigorously pedaled, the chain 111 tendsto pull the rear sprocket 109 toward the front of the bicycle 10 in thedirection H shown in FIG. 2. The pulling of the rear sprocket 109 in thedirection H causes a force to be transmitted upwardly through the seatstay members 88, 90 in the direction A, and a force to be transmitteddownwardly through the chain stay members 96, 98 in the direction I alsoshown in FIG. 2. The transmission of force in the direction A tends topivot the upper rocker 60 upwardly in the direction B, while thetransmission of force in the direction I tends to pivot the lower rocker62 downwardly in a direction opposite the direction F, thus producingthe tension in the alignment rod 150 as previously described.

In addition to the foregoing, due to the configuration of the linkageassembly, the rear wheel 110 is free to accommodate vertical travel as aresult of a vertical shock force despite the linkage assembly beingunder the effect of chain tension. As a result, the present linkagesystem is fully active and can absorb bumps and shocks to identicaldegrees of efficiency regardless of the magnitude of chain tension, andwill neither lock up or squat under the influence of pedaling.

Additional modifications and improvements of the present invention mayalso be apparent to those skilled in the art. Thus, the particularcombination of parts described and illustrated herein is intended torepresent only one embodiment of the invention, and is not intended toserve as limitations of alternative devices within the spirit and scopeof the invention.

What is claimed is:
 1. A bicycle rear suspension linkage system,comprising:an elongate seat tube having upper and lower ends; an upperpivot mount rigidly attached to the upper end of said seat tube; an axlereceiving bracket rigidly attached to the lower end of said seat tube; alower pivot mount rigidly attached to said axle receiving bracket; anupper rocker pivotally connected to said upper pivot mount; a lowerrocker pivotally connected to said lower pivot mount; first and secondseat stay members having upper ends rigidly attached to a seat stay endhousing and lower ends, said seat stay end housing being pivotallyconnected to said upper rocker; first and second chain stay membershaving front ends rigidly attached to a chain stay end housing and backends pivotally connected to the lower ends of said seat stay members,said chain stay end housing being pivotally connected to said lowerrocker; a pair of rear tire axle receiving members rigidly attached tothe lower ends of said seat stay members; a shock absorber comprising:abody portion having first and second ends; and a reciprocable piston rodextending axially from said first end and having a distal end pivotallyconnected to said upper pivot mount; first and second upper link rodshaving top ends pivotally connected to opposed sides of said upperrocker and bottom ends pivotally connected to opposed sides of said bodyportion; an elongate alignment rod having proximal and distal ends, saidproximal end being rigidly attached to the second end of the bodyportion in a manner wherein said alignment and piston rods are coaxiallyaligned; and a lower link rod having a first end pivotally connected tothe distal end of said alignment rod and a second end pivotallyconnected to said chain stay end housing.
 2. The linkage system of claim1 wherein said alignment rod extends through and is guided by at leastone alignment bushing rigidly attached to said seat tube.
 3. The linkagesystem of claim 2 wherein said alignment rod extends through a pair ofalignment bushings rigidly attached to said seat tube.
 4. The linkagesystem of claim 1 wherein the coaxially aligned alignment and pistonrods extend in parallel relation to said seat tube.
 5. The linkagesystem of claim 1 wherein said shock absorber further comprises a springmember extending between said upper pivot mount and said body portion,said piston rod extending axially through said spring member.
 6. Thelinkage system of claim 1 wherein the seat stay members and the upperrocker are adapted to have a greater mechanical advantage in pullingupwardly on the upper link rods, alignment rod and lower link rod thanthe chain stay members and lower rocker have in pulling downwardly onthe lower link rod, alignment rod and upper link rods so as to maintainthe linkage system in tension.
 7. The linkage system of claim 1 whereinthe proximal end of the alignment rod is threadably attached to thesecond end of the body portion.